How do I add a new article to this wiki?

If the page does not already exist then at the bottom of the search results page it will say:

Create the page "search terms" on this wiki!

Click on the red search terms text and save some content to create the new page.

Wanted pages

If you create a wiki link to a page that doesn't exist yet then it will show in red. You'll then be able to follow the link to create the article yourself. It will also show up in Wanted Pages, so if you don't have time to create an article you can at least indicate that it's wanted.